Geographic Range

Euprymna scolopes is a sepiolid squid endemic to the oceanic habitats surrounding the Hawaiian Islands. This squid can greatly affect the relative abundance and geographic distribution of its bacterial symbiont Vibrio fischeri. (Ruby and Ho Lee, 1998)

Habitat

Euprymna scolopes is found in warm, shallow coastal waters 2-4 cm deep. This is unusual because most sepiolid squids reside in very deep water. Euprymna scolopes is often seen laying its eggs on the foundations of coral ridges. During the day, these squid are buried in the sand. At night, they emerge and wade through the sand with their bioluminescent light organ which allows them to see and hunt in the dark. (Nyholm and McFall-Ngai, 1998; Shears, 1988)

Physical Description

Euprymna scolopes is one of the smallest and slimmest sepiolid squids. The mantle plus tentacles measure an average of 35 mm (1.4 in) in length, and weighs an average of 2.76 grams (0.09 oz). The birth mass of a hatchling is an average 0.005 grams (0.00018 oz). Males have slightly larger suckers than females, with thinner posterior mantles. Both sexes have a pair of unique paddle shaped fins that aid in swimming. A feature unique to Euprymna scolopes is the bilobed and bioluminescent light organ present inside the squid’s mantle cavity. This organ, which functions through its interaction with its symbiotic partner Vibrio fischeri, provides light, allowing the squid to hunt its prey at night. This squid also possesses metabracial vesicles, which function as the eyes of this bobtail squid. The vesicles allow the squid to perceive and manipulate the amount of light it can give off, so the squid can camouflage itself in a process known as counterillumination. (Boettcher and Ruby, 1995; Hanlon, et al., 1997)

Development

Euprymna scolopes develops rapidly and grows exponentially. After copulation, there is a 18-26 day embryonic period. The planktonic hatchling first emerges from the egg, and is initially aposymbiotic, meaning it cannot use its light organ. After several days, the hatchling develops into a planktonic paralarva that can partially make use of the light organ. The paralarva develops into a juvenile after ten days, and becomes mature enough to travel into shallower waters. After 130 days, when the squid is a subadult, the light organ fully functions for hunting and camouflage. The squid will have little to no further growth after 180 days. Male and female organisms, which occur in equal numbers, reach sexual maturation 60 days after hatching. Temperature may be a factor in the time to reach full sexual maturity. Interaction with Vibrio fischeri is not required for normal development and growth. (Boettcher and Ruby, 1995; Hanlon, et al., 1997)

Reproduction

There is no information on the mating system of Euprymna scolopes.

Mating is initiated by the male, which grabs the female and places its spermatophore in the female's mantle. The female's mantle will become larger as it is filled with eggs. Mating lasts 30-50 minutes, and occurs mostly at night. Studies have shown that rainfall increases the amount of breeding. There are no specific seasonal breeding intervals for this squid. Females tend to lay eggs in the morning in shallow areas on coral ridges. Clutch sizes vary between 50-200 eggs. It takes an average 30 minutes to lay each clutch of eggs. The number of clutches each female lays varies greatly. After females are finished laying eggs, they cover them with sand and then depart, leaving the offspring to fend for themselves.

Behavior

Euprymna scolopes is most active between dusk and dawn. During this time the organism captures and consumes its prey. Although nocturnal, E. scolopes can still be active in daylight. When not hunting, E. scolopes usually buries itself in the sand substrate or is covered in at least a small layer of sand to camouflage itself from predators. This species also uses counterillumination, another form of camouflage where the squid controls the amount of light from the light organ to match the light emitted from the light source in the area.

Communication and Perception

Euprymna scolopes has a symbiotic relationship with a bioluminescent marine bacterium called Vibrio fischeri. This mutualistic relationship begins early in the life stages of the squid and development of the light organ results. The squid controls the amount and timing of the bioluminescence given off by the bacteria. When the bacteria are found outside of this mutualistic relationship the strength of the light given off is not nearly as strong as it is when it is housed inside the light organ of E. scolopes. This light organ is generally used for a specialized behavior known as counterillumination, which allows the organism to camouflage themselves and avoid predators. (Boettcher and Ruby, 1990; Jones and Nishiguchi, 2004; McFall-Ngai and Ruby, 1998)

Food Habits

The primary component of the adult E. scolopes diet is mysid shrimp, and younger squids will also consume crustaceans in the genus Artemia. Euprymna scolopes is a cryptic "sit and wait" predator. The squid buries itself in the sand with its tentacles and wait for prey to pass by. Euprymna scolopes attacks by aiming all the arms at the prey and strikes using the two tentacles. If the squid misses the prey it remains buried and waits for another organism. (Archetti, et al., 2011; Fleisher and Case, 1995; Moynihan, 1983)

Predation

As previously mentioned, Euprymna scolopes uses counterillumination to camouflage from predators. Another defense mechanism is burying itself in an outer covering made of sand. Last, the squid releases an amount of ink when they sense a stimuli indicating the presence of a predator. The pool of ink is used to deceive the predator and prevent attack by resembling the shape of the squid. Known predators of E. scolopes include lizardfish (family Synodontidae), barracuda (genus Sphyraena), and Hawaiian monk seal (Monachus schauinslandi). (Jones and Nishiguchi, 2004; Lee, et al., 2009; Visick and McFall-Ngai, 2000)

Contributors

Eric Hasbun (author), The College of New Jersey, Will Wardell (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Renee Mulcrone (editor), Special Projects.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

photic/bioluminescent

generates and uses light to communicate

polarized light

light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.